1. Field of the Invention
The present invention relates to a projection optical system inspecting method and inspection apparatus, and a projection optical system manufacturing method, and more particularly relates to a projection optical system inspecting method and inspection apparatus, and a projection optical system manufacturing method, wherein the projection optical system is provided with an exposure apparatus, used in a lithographic process, that projects an image of a pattern formed on a mask onto a substrate.
2. Description of Related Art
In the fabrication of microdevices, such as semiconductor devices, imaging devices, liquid crystal devices, and thin film magnetic heads, an exposure apparatus is used that transfers the image of a pattern formed on a mask or reticle (hereinafter, these are generically referred to as masks) onto a wafer, a glass plate, or the like (hereinafter, these are generically referred to as substrates), which is coated with a photosensitive agent such as a photoresist. Exposure apparatuses are broadly classified as: full exposure type projection exposure apparatuses, such as steppers, which are widely used when manufacturing, for example, semiconductor devices, and the like, whereon extremely fine patterns are formed; and scanning exposure type projection exposure apparatuses, such as step-and-scan systems, which are widely used when manufacturing, for example, large area liquid crystal devices; furthermore, each of these exposure apparatuses normally comprises a projection optical system for transferring the pattern image of the mask onto the substrate.
Because a microdevice is generally fabricated by the formation of a plurality of patterns in layers, when fabricating a microdevice using an exposure apparatus, the pattern image of the mask must be faithfully projected with high resolution onto the substrate in a state where the pattern image of the mask to be projected is accurately aligned with the pattern previously formed on the substrate. Consequently, there is demand for a projection optical system in which aberrations are adequately controlled, and that has an exceptionally superior optical performance with high resolution. The optical performance of a projection optical system is inspected by generating an ideal spherical wave, and then e.g., by the following procedure. Mainly, the performance of the projection optical system is inspected by splitting the generated ideal spherical wave into a measuring beam and a reference beam, entering only the measuring beam into the projection optical system, reflecting the measuring beam that transmitted through the projection optical system by a reflecting member having a concave spherical mirror disposed on the image plane side of the projection optical system, interfering the measuring beam that once again transmitted through the projection optical system with the reference beam which did not transmit through the projection optical system, and analyzing the interference fringes thereby obtained. For details on the conventional method of inspecting a projection optical system, please refer to, for example, Japanese Unexamined Patent Application, First Publication No. 2002-296005 and Japanese Unexamined Patent Application, First Publication No. H10-160582.
Incidentally, in recent years there has been a rise in the demand for increasingly finer patterns formed on substrates because, to cite the example of manufacturing semiconductor devices, the increasing fineness of the pattern increases the number of semiconductor devices fabricated from a single substrate. Consequently, the fabrication cost of the semiconductor devices decreases, and the semiconductor devices can be made more compact. Additionally, the increasing fineness allows the operating frequency to be increased, and reduces power consumption. Current CPUs (central processing units) are fabricated with a process rule of approximately 0.1 to 0.2 μm, but in the future will be fabricated with a process rule of less than 0.1 μm.
To form a fine pattern, the wavelength of the illumination light that illuminates the mask during exposure must be shortened, and the numerical aperture (NA) of the projection optical system must be set high. Because shortening the wavelength of the illumination light restricts the glass material that can be used for the lens of the projection optical system, the degrees of freedom in the design of the projection optical system unfortunately decrease, and the cost of the projection optical system itself unfortunately increases. Consequently, in recent years, a liquid immersion type projection optical system has been proposed that raises the resolution by filling a liquid, having a refractive index higher than gas (air or nitrogen gas), between the projection optical system and the substrate, leading to an increasingly strong demand to accurately inspect (measure) the optical performance of this liquid immersion type projection optical system.
The present invention was made by taking such circumstances into consideration, and has an object to provide a projection optical system inspecting method and inspection apparatus, and a projection optical system manufacturing method, that can easily and accurately inspect the optical performance of a liquid immersion type projection optical system, wherein a liquid is disposed on the image plane side.